LTE (Long Term Evolution), which is standardized by the third generation partnership project (3GPPP), may be employed in each of frequency division duplex (FDD) and time division duplex (TDD). Because of easiness in frequency configuration and changeability of proportions of radio resources for uplink and downlink, it is envisaged that TDD is employed in many systems in future for the effective utilization of frequency.
In TDD, a link direction (for example, downlink, and uplink) is set for each subframe. More specifically, a plurality of TDD configurations (or a plurality of uplink and downlink configurations) each indicating the link direction of each subframe are prepared in advance, and one of the TDD configurations is used. For example, a communication business operator selects one TDD configuration from among seven TDD configurations defined in the LTE technology standard, and sets it in a fixed manner. Further, 3GPP is studying a method which dynamically sets an optimal TDD configuration in response to traffic in a cell, aiming at improving throughput of the entire network in future. Various technologies related to dynamic setting of TDD configuration have been proposed.
For example, Patent Literature 1 discloses a technology which adjusts timing of acknowledgement and negative acknowledgement (ACK and NACK) for a hybrid automatic repeat request (HARQ), when dynamically setting a TDD configuration.